In general, diesel engines are advantageous because they have various uses due to their high power and ability to be operated even under high loads. However, since exhaust gases discharged from such diesel engines are a major source of air pollution, their allowable discharge standard becomes more and more strict throughout the world. The main pollutants from diesel engines include fine soot particulates, hydrocarbons, carbon monoxide, soluble organic solvents, and nitrogen oxides. In particular, the soot particulates and NOx directly impact life, such as increasing a generation rate of cancer of the respiratory organs, and thus, diesel exhaust gases are classified as carcinogenic material by IARC (The International Agency for Research on Cancer) and USEPA (The US Environmental Protection Agency). Hence, various treatment techniques for removing diesel exhaust gases have been devised. Such techniques are largely divided into engine improvement techniques and post-treatment techniques. Of these techniques, as post-treatment techniques, methods of removing soot particulates and of removing NOx have chiefly been developed. However, the former engine improvement techniques need to be more urgently realized.
At present, the removal of soot particulates from exhaust gases chiefly depends on regeneration processes following the collection. However, the above process is disadvantageous because a filter for use in the removal of soot particulates may be internally clogged by cake-like particulates over time. With the goal of prolonging the lifetime of the filter, the combustion of the adsorbed soot particulates is periodically required. During the past several years, many attempts to regenerate a filter have been vigorously made, and the following techniques have been actualized:                (1) Combustion of soot using an external heat source, such as a heater or a burner;        (2) Formation of combustion conditions of soot using engine control, such as an increase in exhaust gas temperature; and        (3) Reduction in a combustion temperature of soot using a catalyst.        
Particularly, regeneration methods using a catalyst are advantageous because high regeneration efficiency can be simply realized without additional power or energy consumption. The above methods are typically realized by coating a filter with a catalyst including a precious metal component such as platinum (Pt) or palladium (Pd) (U.S. Pat. Nos. 6,685,900, 6,274,107, and 5,911,961, and Korean Patent Laid-open Publication Nos. 2003-0028121, 2003-0007993, 2003-0091346, and 2004-0095166). However, since the use of a precious metal in a high concentration of about 2.5-7 g/L is required to decrease the oxidation temperature of soot, the preparation cost increases and the amount of soot particulates is somewhat increased due to the formation of sulfur oxides. As a non-precious metal catalyst, an NOx reduction catalyst including ZnAl2O3 as Spinel-based crystals is disclosed (U.S. Pat. No. 5,876,681), and a Perovskite type metal oxide catalyst including a small amount of platinum is disclosed (U.S. Pat. No. 5,622,680). Although the above catalysts are said to take charge of effective oxidation of soot particulates, the development of more effective catalysts usable at lower temperatures is necessary, taking into account that the exhaust gas temperature of diesel engines ranges from 150 to 350° C.
In addition, soot particulates may be formed due to the incomplete combustion in boilers or incinerators using fossil fuel, and as well, the soot particulates thus formed are precipitated in a boiler pipe or an exhaust pipe, thus decreasing the combustion efficiency and requiring the washing of the exhaust pipe. Therefore, there is urgently required the development of a catalyst that is used to oxidize the precipitated soot particulates to be removed, does not deteriorate at high temperatures, and is not poisoned even in the presence of SO2.